The plastic additive has been vilified by environmental advocacy groups. But the chemical had no effect on rats fed thousands of times the amount a typical person ingests, government scientists are reporting in the journal Toxicological Sciences.

Scientists agree that in large doses, BPA can act a bit like the hormone estrogen. But there's been a lot of debate about whether the tiny amounts found in people have the potential to cause problems.

BPA has received a lot of attention because the chemical leaches out of many products, including polycarbonate water bottles and the lining of metal food containers. As a result, "Nearly everyone in the U.S. will have traces of BPA in their urine," Doerge says.

So Doerge and his colleagues have been working with scientists from the National Toxicology Program at the National Institutes of Health to see if there are any effects from this low-level exposure.

In their most recent study, the researchers exposed rats to BPA starting a few days after conception and continuing through sexual maturity. Doses ranged from about 70 times the amount that Americans typically get through their diet to millions of times that amount.

And even when rats got more than 70,000 times what a typical American ingests, there was no change in body weight, reproductive organs or hormone levels, the scientists reported. "In the low-dose range, there really were no biologically significant changes observed at all," Doerge says.

It was only when exposures were millions of times higher than what people typically get that the scientists saw changes like those caused by the body's own sex hormones.

To double-check the results, the scientists also looked at how BPA was interacting with estrogen receptors — the part of a cell that usually responds to estrogen. And once again it was only the highest doses that produced interactions.

The results bolster previous studies by government researchers showing that people's exposure to BPA is lower than previously estimated and that the human body is really good at inactivating and eliminating BPA. But they are at odds with some smaller and less rigorous academic studies.

Some of the academic scientists who did those studies have already called the new government study flawed. They say it failed to look at things like brain development. They also say the results were compromised because even the "control" animals in the study had trace amounts of BPA in their bodies.

That sort of response is pretty typical in the debate over BPA and other hormonelike chemicals known as endocrine disruptors, says David Ropeik, a Harvard instructor and author of the book How Risky is it, Really? "The endocrine disruption issue has evoked some of the most visceral and ugly attacks among scientists of any scientific issue recently," he says.

For example, when the European Food Safety Authority concluded a few weeks ago that BPA is far less risky than some advocacy groups had suggested, "the endocrine disruption movement said, 'Oh my God, they're all corrupt. They're all taking corporate money,' " Ropeik says.

Lively debate is a natural part of science playing out in the public realm. But this sort of allegation may help undermine trust in regulatory agencies and their scientists, Ropeik says.

And it may leave consumers perplexed about what chemicals like BPA are actually doing in the body. In that case, Ropeik recommends referring back to the best science available.

Transcript

AUDIE CORNISH, HOST:

From NPR News, this is ALL THINGS CONSIDERED. I'm Audie Cornish.

MELISSA BLOCK, HOST:

And I'm Melissa Block.

Next, an update on the plastic additive known as bisphenol-A, or BPA. Government scientists have spent several years trying to figure out whether BPA in food poses a risk to consumers. Well, now those scientists say they've found little to suggest that the chemical is harming us.

NPR's Jon Hamilton reports.

JON HAMIILTON, BYLINE: Scientists agree that in large doses, BPA can act a bit like the hormone estrogen. But there's been a lot of debate about whether the tiny amounts found in people have the potential to cause problems.

Daniel Doerge, a research chemist with the Food and Drug Administration, says it's an important question because the chemical leaches out of so many products, including plastic water bottles and food containers.

DANIEL DOERGE: Nearly everyone in the U.S. will have traces of BPA in their urine, indicating this low level of exposure through food.

HAMIILTON: So Doerge and his colleagues at FDA's National Center for Toxicological Research have been working with scientists from the National Toxicology Program at the NIH, to see if there are any effects from this low-level exposure. In a new study, published in the journal Toxicological Sciences, the team exposed rats to BPA. The exposure began a few days after conception and continued through sexual maturity at 90 days. Some rats got a little BPA. Others got a lot.

Doerge says even the lowest amount was much greater than the amount a typical American gets through their diet.

DOERGE: It's about 70 times higher at this lowest dose. So it's, you know, millions of times higher at the highest dose.

HAMIILTON: So what did you find?

DOERGE: Not much.

HAMIILTON: Doerge says even when rats got more than 70,000 times what a typical American ingests, there was no change in body weight or reproductive organs or hormone levels.

DOERGE: In the low-dose range, there really were no biologically significant changes observed at all. It was only at the two highest doses where there were effects on reproductive tissues and other endpoints.

HAMIILTON: It took millions of times the dose consumers get to produce effects similar to those of the body's own sex hormones. To double check those results, the scientists looked at how BPA was interacting with estrogen receptors, the part of a cell that usually responds to estrogen. And once again, it was only the highest doses that produced interactions. The results bolster previous studies by government researchers, showing that people's exposure to BPA is lower than previously estimated. They also found that the human body is really good at inactivating and eliminating BPA.

So what does all this mean for consumers? Doerge puts it this way.

DOERGE: The results both support and extend the conclusion from the U.S. Food and Drug Administration that BPA is safe as currently used. And I should point out that a similar conclusion was just recently reached by the European Food Safety Authority.

HAMIILTON: The results are at odds with some smaller and less rigorous academic studies. And some of the scientists who did those studies have already called the new government research flawed. They say it failed to look at things like brain development.

David Ropeik, a Harvard instructor and consultant in risk perception, says that sort of response is pretty typical in the debate over BPA and other hormone-like chemicals known as endocrine disruptors.

DAVID ROPEIK: The endocrine disruption issue has evoked some of the most visceral and ugly attacks among scientists of any scientific issue recently.

HAMIILTON: Ropeik says a recent experience in Europe shows how these attacks often ignore the science underlying regulatory decisions.

ROPEIK: The European Food Safety Administration did what the FDA did: reviewed all the science and said at the doses we get it, BPA is probably not the risk that some people fear. At which point, the endocrine disruption movement said: Oh, my God, they're all corrupt. They're all taking corporate money.

HAMIILTON: Ropeik says that sort of allegation may undermine trust in regulatory agencies and their scientists. But it doesn't help consumers understand what chemicals like BPA are actually doing in the body.